5:15 PM - 6:45 PM
[MIS12-P03] Paleoenvironmental and vegetation changes over the past several hundred years reconstructed from lake sediments of Lake Buir, eastern Mongolia (Preliminary result)
Keywords:Pollen analysis, Vegetation change, Permafrost, Summer monsoon, Mongolia
Lake Buir in eastern Mongolia is located at the boundary between the southern limit of the permafrost and the desert zone, and is classified as a steppe climate zone. In addition, it is located in the marginal zone of the East Asian summer monsoon; therefore, this region is considered to be sensitive to climate change. In this study, we tried to reconstruct paleoenvironmental and vegetation changes in eastern Mongolia over the past several hundred years based on elemental composition and pollen assemblages in the sediments of Lake Buir.
The sample for this study is a gravity core (80 cm long) collected in February 2021 at Lake Buir. Lake Buir is freshwater lake with an average depth of 8 m located on the border between Mongolia and China. There is an inflow river called Khalkha River. There is also one outflow river that flows into downstream side of Lake Hulun in northeastern China. The sediments consist of dark greenish gray clay. Based on the 137Cs and 210Pb measurement, a peak of 137Cs observed at 12 cm depth is interpreted as 1963, and an increase of 137Cs at 24 cm depth is interpreted as 1952. If the sedimentation rate is constant, it is suggested that the deepest 80 cm section of the core is approximately 234-400 years ago. Pollen analysis was performed using samples of each 1cm. We also conducted high-resolution elemental composition analysis at 0.5-mm intervals using an XRF core scanner (Itrax).
The results of elemental composition analysis indicate that the lower 60-80 cm of the sediments consist of a slightly smaller grain size than the upper 0-60 cm based on the Zr/Rb ratio. The Ca concentrations are slightly higher in the 7-19 cm, 47-67 cm, and 79-80 cm intervals. Pollen analysis indicated that Artemisia (60-70%) and Chenopodiaceae (15-25%) are dominated, so the steppe vegetation are mostly prevailed. In the case of woody pollens, Betula (2-10%) and Pinus complexus subgenus (1-3%) were included. The Artemisia/Chenopodiaceae ratio was high in the uppermost 0-45 cm, while it become lower in the 45-80 cm. The Betula tend to increase in the uppermost 0-6 cm. These lines of evidence suggest that the environment was arid environment during the Little Ice Age of the 17th and 18th centuries, while it became to slightly wetter environment in the 19th and 20th centuries. Betula are increased in the latter half of the 20th century.
We are going to constrain better chronological model of the core based on 14C dating to reconstruct the paleoenvironment and vegetation evolution of eastern Mongolia. We also plan to make an integrated comparison with pollen records from the Sangiin Dalai Lake in northwestern Mongolia and other lakes in southern and northern Mongolia, northeastern China, and other areas in the vicinity.
The sample for this study is a gravity core (80 cm long) collected in February 2021 at Lake Buir. Lake Buir is freshwater lake with an average depth of 8 m located on the border between Mongolia and China. There is an inflow river called Khalkha River. There is also one outflow river that flows into downstream side of Lake Hulun in northeastern China. The sediments consist of dark greenish gray clay. Based on the 137Cs and 210Pb measurement, a peak of 137Cs observed at 12 cm depth is interpreted as 1963, and an increase of 137Cs at 24 cm depth is interpreted as 1952. If the sedimentation rate is constant, it is suggested that the deepest 80 cm section of the core is approximately 234-400 years ago. Pollen analysis was performed using samples of each 1cm. We also conducted high-resolution elemental composition analysis at 0.5-mm intervals using an XRF core scanner (Itrax).
The results of elemental composition analysis indicate that the lower 60-80 cm of the sediments consist of a slightly smaller grain size than the upper 0-60 cm based on the Zr/Rb ratio. The Ca concentrations are slightly higher in the 7-19 cm, 47-67 cm, and 79-80 cm intervals. Pollen analysis indicated that Artemisia (60-70%) and Chenopodiaceae (15-25%) are dominated, so the steppe vegetation are mostly prevailed. In the case of woody pollens, Betula (2-10%) and Pinus complexus subgenus (1-3%) were included. The Artemisia/Chenopodiaceae ratio was high in the uppermost 0-45 cm, while it become lower in the 45-80 cm. The Betula tend to increase in the uppermost 0-6 cm. These lines of evidence suggest that the environment was arid environment during the Little Ice Age of the 17th and 18th centuries, while it became to slightly wetter environment in the 19th and 20th centuries. Betula are increased in the latter half of the 20th century.
We are going to constrain better chronological model of the core based on 14C dating to reconstruct the paleoenvironment and vegetation evolution of eastern Mongolia. We also plan to make an integrated comparison with pollen records from the Sangiin Dalai Lake in northwestern Mongolia and other lakes in southern and northern Mongolia, northeastern China, and other areas in the vicinity.